Formation of polyesters consisting of medium-chain-length 3-hydroxyalkanoic acids from gluconate by Pseudomonas aeruginosa and other fluorescent pseudomonads

Abstract

Pseudomonas aeruginosa PAO and 15 other strains of this species synthesized a polyester with 3-hydroxydecanoate as the main constituent (55 to 76 mol%) if the cells were cultivated in the presence of gluconate and if the nitrogen source was exhausted; 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydodecanoate were minor constituents of the polymer. The polymer was deposited in granules within the cell and amounted to 70% of the cell dry matter in some strains. Among 55 different strains of 41 Pseudomonas species tested, P. aureofaciens (21.6% of cellular dry matter), P. citronellolis (78.0%), P. chlororaphis (8.5%), P. marginalis (11.4%), P. mendocina (50.7%), P. putida (33.5%), and Pseudomonas sp. strain DSM 1650 (54.6%) accumulated this type of polymer at significant levels (greater than 5%) during cultivation on gluconate. In two strains of P. facilis and P. fluorescens, as well as in one strain of P. syringae, this polymer was detected as a minor constituent (much less than 5%). All other strains accumulated either poly(3-hydroxybutyrate) or a polymer consisting mainly of 3-hydroxyoctanoate with octanoate but no polyester with gluconate as the carbon source. Only a few species (e.g., P. stutzeri) were unable to accumulate poly(hydroxyalkanoic acids) (PHA) at all. These results indicated that the formation of PHA depends on a pathway which is distinct from all other known PHA-biosynthetic pathways. The polyesters accumulated by gluconate- or octanoate-grown cells of recombinant strains of P. aeruginosa and P. putida, which harbored the Alcaligenes eutrophus poly(3-hydroxybutyrate)biosynthetic genes, contained 3-hydroxybutyrate as an additional constituent.